Printed wiring board and method for manufacturing printed wiring board

ABSTRACT

A printed wiring board includes a core substrate having a penetrating hole penetrating through the core substrate and having a first insulation layer, a second insulation layer and an insulative substrate interposed between the first and second layers, a first circuit formed on a surface of the core, a second circuit formed on opposite surface of the core, and a through-hole conductor formed in the penetrating hole of the core and connecting the first and second circuits. The penetrating hole has first and second opening portions, the first opening portion becomes thinner from the first surface toward the second surface, the second opening portion becomes thinner from the second surface toward the first surface, and the first and second insulation layers are comprised of resin materials easier to be processed by laser than resin material of the insulative substrate under same conditions of the laser.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claims thebenefit of priority to U.S. application Ser. No. 13/618,427, filed Sep.14, 2012, which is a continuation application of U.S. application Ser.No. 12/954,052, filed Nov. 24, 2010, Now U.S. Pat. No. 8,304,657,granted Nov. 6, 2012, which is based upon and claims the benefit ofpriority to U.S. Application No. 61/317,408, filed Mar. 25, 2010. Theentire contents of these applications are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a printed wiring board and itsmanufacturing method. A printed wiring board of the present inventionincludes a core substrate having a penetrating hole made up of a firstopening portion and a second opening portion, first circuit and secondcircuits formed on the core substrate, and a through-hole conductorformed in the penetrating hole and connecting the first and secondcircuits.

2. Discussion of the Background

Japanese Laid-Open Patent Publication 2006-41463 describes forming apenetrating hole made up of a first blind hole and a second blind holein a dielectric layer. The penetrating hole in Japanese Laid-Open PatentPublication 2006-41463 is formed as an hourglass and is filled withconductive material. The contents of this publication are incorporatedherein by reference in their entirety.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, a printed wiring boardincludes a core substrate having a first surface and a second surface onthe opposite side of the first surface, the core substrate having apenetrating hole penetrating through the core substrate between thefirst surface and the second surface, a first circuit formed on thefirst surface of the core substrate, a second circuit formed on thesecond surface of the core substrate, and a through-hole conductorformed in the penetrating hole of the core substrate and connecting thefirst circuit and the second circuit. The penetrating hole has a firstopening portion and a second opening portion. The first opening portionof the penetrating hole becomes thinner from the first surface towardthe second surface. The second opening portion of the penetrating holebecomes thinner from the second surface toward the first surface. Thefirst opening portion has a first opening on the first surface of thecore substrate and has a first portion including the first opening and asecond portion contiguous to the first portion of the first openingportion. The second opening portion has a second opening on the secondsurface of the core substrate and has a first portion including thesecond opening and a second portion contiguous to the first portion ofthe second opening portion. The first portion and second portion of thefirst opening portion form inner walls of the first opening portionwhich bend inward with respect to the periphery of the penetrating holeat the boundary between the first portion and second portion of thefirst opening portion. The first portion and second portion of thesecond opening portion form inner walls of the second opening portionwhich bend inward with respect to the periphery of the penetrating holeat the boundary between the first portion and second portion of thesecond opening portion.

According to another aspect of the present invention, a method formanufacturing a printed wiring board includes preparing a core substratehaving a first surface and a second surface on the opposite side of thefirst surface, forming a penetrating hole having a first opening portionand a second opening portion in the core substrate such that the firstopening portion becomes thinner from the first surface of the coresubstrate toward the second surface and that the second opening portionbecomes thinner from the second surface of the core substrate toward thefirst surface, forming a first circuit on the first surface of the coresubstrate, forming a second circuit on the second surface of the coresubstrate, and forming a plated film in the penetrating hole such that athrough-hole conductor connecting the first circuit and the secondcircuit is formed. The first opening portion has a first opening on thefirst surface of the core substrate and has a first portion includingthe first opening and a second portion contiguous to the first portionof the first opening portion. The second opening portion has a secondopening on the second surface of the core substrate and has a firstportion including the second opening and a second portion contiguous tothe first portion of the second opening portion. The first portion andsecond portion of the first opening portion form inner walls of thefirst opening portion which bend inward with respect to the periphery ofthe penetrating hole at the boundary between the first portion andsecond portion of the first opening portion. The first portion andsecond portion of the second opening portion form inner walls of thesecond opening portion which bend inward with respect to the peripheryof the penetrating hole at the boundary between the first portion andsecond portion of the second opening portion.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the invention and many of the attendantadvantages thereof will be readily obtained as the same becomes betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings, wherein:

FIGS. 1(A) through 1(E) are views showing the steps of a method formanufacturing a multilayer printed wiring board according to the firstembodiment;

FIGS. 2(A) through 2(C) are views showing the steps of a method formanufacturing a multilayer printed wiring board according to the firstembodiment;

FIGS. 3(A) through 3(D) are views showing the steps of a method formanufacturing a multilayer printed wiring board according to the firstembodiment;

FIGS. 4(A) through 4(D) are views showing the steps of a method formanufacturing a multilayer printed wiring board according to the firstembodiment;

FIGS. 5 (A) through 5(C) are views showing the steps of a method formanufacturing a multilayer printed wiring board according to the firstembodiment;

FIG. 6 is a cross-sectional view of a multilayer printed wiring boardaccording to the first embodiment;

FIG. 7 is a view showing angles between a first surface of a coresubstrate and inner walls of a penetrating hole;

FIG. 8 are views showing cross sections of penetrating holes in areference example and in the first embodiment;

FIG. 9 are views showing inner diameters of a penetrating hole in thefirst embodiment;

FIGS. 10(A) and 10(C) show a through-hole conductor in a referenceexample, and FIGS. 10(B), 10(D), 10(E) and 10(F) show through-holeconductors in the first embodiment;

FIGS. 11(A), 11(B), 11(C) and 11(D) show penetrating holes in the firstembodiment, (A-1) is a plan view showing a first surface of a coresubstrate in the first embodiment, and (A-2) is a plan view showing asecond surface of the core substrate in the first embodiment;

FIGS. 12(A) and 12(B) are views schematically showing energy intensityof a laser, and FIG. 12(C) is a view showing an example where apenetrating hole is bent in a reinforcing material;

FIG. 13 are views showing other steps for manufacturing a printed wiringboard of the first embodiment;

FIG. 14 are cross-sectional views showing penetrating holes in the firstembodiment;

FIG. 15 are views to illustrate the positions to irradiate laser beams;and

FIG. 16 is a cross-sectional view showing a multilayer printed wiringboard according to the second embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The embodiments will now be described with reference to the accompanyingdrawings, wherein like reference numerals designate corresponding oridentical elements throughout the various drawings.

First Embodiment

Multilayer printed wiring board 10 of the first embodiment is describedwith reference to FIG. 6. FIG. 6 shows a cross-sectional view ofmultilayer printed wiring board 10. In multilayer printed wiring board10, first circuit (34A) is formed on a first surface of core substrate30, and second circuit (34B) is formed on a second surface. Firstcircuit (34A) has first conductive circuit (34AC) and first land (34AL),and second circuit (34B) has second conductive circuit (34BC) and secondland (34BL). The first conductive circuit and the second conductivecircuit are connected by through-hole conductor 36. The first land andthe second land are connected by through-hole conductor 36. Upper-layerfirst interlayer resin insulation layer (50A) is formed on the firstsurface of core substrate 30 and on the first circuit. Upper-layer firstinterlayer resin insulation layer (50A) has a first surface and a secondsurface opposite the first surface. The second surface of upper-layerfirst interlayer resin insulation layer (50A) faces the first surface ofthe core substrate. Conductive circuit (58A) is formed on the firstsurface of upper-layer first interlayer resin insulation layer (50A).Conductive circuit (58A) on upper-layer first interlayer resininsulation layer (50A) and the first circuit or the through-holeconductor are connected by via conductor (60A), which penetrates throughupper-layer first interlayer resin insulation layer (50A).

Lower-layer first interlayer resin insulation layer (50B) is formed onthe second surface of core substrate 30 and on the second circuit.Lower-layer first interlayer resin insulation layer (50B) has a firstsurface and a second surface opposite the first surface. The secondsurface of lower-layer first interlayer resin insulation layer (50B)faces the second surface of the core substrate. Conductive circuit (58B)is formed on the first surface of lower-layer first interlayer resininsulation layer (50B). Conductive circuit (58B) on lower-layer firstinterlayer resin insulation layer (50B) and the second circuit or thethrough-hole conductor are connected by via conductor (60B), whichpenetrates through lower-layer first interlayer resin insulation layer(50B).

Upper-layer solder-resist layer (70A) is formed on the first surface ofupper-layer first interlayer resin insulation layer (50A), andlower-layer solder-resist layer (70B) is formed on the first surface oflower-layer first interlayer resin insulation layer (50B). Upper andlower solder-resist layers (70A, 70B) have openings (71A, 71B) thatexpose via conductors (60A, 60B) and conductive circuits (58A, 58B). Topsurfaces of the via conductors and the conductive circuits exposedthrough openings (71A, 71B) function as solder pads (72A, 72B). Solderbumps (78A, 78B) are formed on solder pads (72A, 72B).

A magnified view of through-hole conductor 36 formed in core substrate30 in FIG. 6 is shown in FIG. 10(B).

Core substrate 30 has insulative substrate 31 having main surface (31A)and secondary surface (31B) opposite the main surface, first resininsulation layer (32A) formed on the main surface of insulativesubstrate 31, and second resin insulation layer (32B) formed under thesecondary surface. Core substrate 30 has penetrating hole 33 whichpenetrates through the core substrate. First resin insulation layer(32A) has a front surface and a back surface opposite the front surface,and the back surface faces the main surface. Second resin insulationlayer (32B) has an upper surface and a lower surface opposite the uppersurface, and the upper surface faces the secondary surface. The coresubstrate has a first surface and a second surface opposite the firstsurface; and the first surface corresponds to the front surface and thesecond surface corresponds to the lower surface. Insulative substrate 31is preferred to contain a reinforcing material, but the first resininsulation layer (32A) and second resin insulation layer (32B) arepreferred not to contain a reinforcing material. As for a reinforcingmaterial, glass cloth, aramid fiber or the like may be used. First andsecond resin insulation layers (32A, 32B) may contain inorganic fillerssuch as silica and alumina. Through-hole conductor 36 is made of theplated metal filled in penetrating hole 33. FIG. 11 show penetratinghole 33 for a through-hole conductor. Penetrating hole 33 has firstopening portion (33A) formed by irradiating a laser from first surface(30A) of core substrate 30, and second opening portion (33B) formed byirradiating a laser from second surface (30B) of the core substrate.FIG. 11(A-1) is a plan view of the first surface of the core substrate,and FIG. 11(A-2) is a plan view of the second surface of the coresubstrate. First opening portion (33A) has first opening (33A-A) on thefirst surface of the core substrate, and second opening portion (33B)has second opening (33B-B) on the second surface of the core substrate.First opening portion (33A) and second opening portion (33B) are joinedinside insulative substrate 31. First opening portion (33A) becomesthinner from the first surface of the core substrate toward the secondsurface; and second opening portion (33B) becomes thinner from thesecond surface of the core substrate toward the first surface. FIG. 11are cross-sectional views obtained by slicing penetrating hole 33 with aplane which passes through the gravity center of the first opening andincludes a straight line (first gravity line) (G1) perpendicular to thefirst surface of the core substrate. As shown in FIG. 11, the innerwalls of the first opening portion bend inward at the interface of thefirst resin insulation layer and the insulative substrate; and the innerwalls of the second opening portion bend inward at the interface of thesecond resin insulation layer and the insulative substrate. Such bendingdirections indicate directions toward the first gravity line.

A straight line passing through the gravity center of the first openingand perpendicular to the first surface of the core substrate may beoffset from a straight line (second gravity line) (G2) passing throughthe gravity center of the second opening and perpendicular to the firstsurface of the core substrate (FIG. 11(B)). The first gravity line andthe second gravity line are not required to overlap. In such a case, itis easier to fill a penetrating hole with plating. The area where afirst opening portion and a second opening portion are connectedincreases, and the connection reliability of the through-hole conductoris enhanced.

The first opening portion has a third opening at the junction of the(first-1) opening portion and the (first-2) opening portion. The secondopening portion has a fourth opening at the junction of the (second-1)opening portion and the (second-2) opening portion. A straight line (thethird gravity line) (G3) passing through the gravity center of the thirdopening and perpendicular to the first surface of the core substrate maybe offset from the first gravity line. The first gravity line and thethird gravity line are not required to overlap. A straight line (fourthgravity line) (G4) passing through the gravity center of the fourthopening and perpendicular to the first surface of the core substrate maybe offset from the second gravity line. The second gravity line and thefourth gravity line are not required to overlap. Penetrating hole 33tends to fill with plating film, and voids are less likely to occur inthe through-hole conductor. The reliability of the through-holeconductor increases. FIG. 7 shows a cross-sectional view of apenetrating hole obtained in a case where the first gravity line and thethird gravity line are offset. Inner walls (X, Y) facing each other in apenetrating hole make different angles (θ1, θ2) to the first surface ofthe core substrate. When a penetrating hole is filled with plated film,the penetrating hole is gradually filled with plated film starting frominner wall X and inner wall Y. If angle (θ1) formed between inner wall Xand the first surface of the core substrate is different from angle (θ2)formed between inner wall Y and the first surface of the core substrate,it is thought that the plating solution supplied into the penetratinghole along the plated film on inner wall X and the plating solutionsupplied into the penetrating hole along the plated film on inner wall Yenters the penetrating hole from different directions. Also, it isthought that the plating solution is supplied into the penetrating holefrom different directions. The plating solution in the penetrating holetends to circulate, and the penetrating hole tends to be filled withplating. When a penetrating hole is filled with electrolytic platedfilm, since deposition speed is fast in electrolytic plating, voids tendto occur in the electrolytic plated film. However, when the firstgravity line and the third gravity line are offset, since the platingsolution in the opening portion tends to circulate, the first openingportion tends to fill with plated film. In the same manner, when thesecond gravity line and the fourth gravity line are offset, the secondopening portion tends to fill with plated film.

The first, second, third and fourth gravity lines may all be offset fromeach other. It is not required that the first, second, third and fourthgravity lines all overlap. The same effects are achieved as above.

When a core substrate is formed with an insulative substrate and with afirst resin insulation layer and a second resin insulation layersandwiching the insulative substrate, the third opening tends to beformed on the interface of the insulative substrate and the first resininsulation layer, and the fourth opening tends to be formed on theinterface of the insulative substrate and the second resin insulationlayer.

A first opening portion is made up of (first-1) opening portion (33A-1)and (first-2) opening portion (33A-2). When the degree at which the(first-1) opening portion becomes thinner from the first surface of thecore substrate toward the second surface is (ΔW1), and the degree atwhich the (first-2) opening portion becomes thinner from the firstsurface of the core substrate toward the second surface is (ΔW2), (ΔW1)is set smaller than (ΔW2). Also, a second opening portion is made up of(second-1) opening portion (33B-1) and (second-2) opening portion(33B-2). When the degree at which (second-1) opening portion (33B-1)becomes thinner from the second surface of the core substrate toward thefirst surface is (ΔW3), and the degree at which the (second-2) openingportion becomes thinner from the second surface of the core substratetoward the first surface is (ΔW4), (ΔW3) is set smaller than (ΔW4).

When a core substrate is formed with an insulative substrate and with afirst resin insulation layer and a second resin insulation layersandwiching the insulative substrate, a (first-1) opening portion islikely formed in the first resin insulation layer, a (first-2) openingportion and a (second-2) opening portion is likely formed in theinsulative substrate, and a (second-1) opening portion is likely formedin the second resin insulation layer. In such situations, (ΔW1) is thedegree at which the (first-1) opening portion becomes thinner from thefront surface of the first resin insulation layer toward the backsurface; (ΔW2) is the degree at which the (first-2) opening portionbecomes thinner from the main surface of the insulative substrate towardthe secondary surface; (ΔW4) is the degree at which the (second-2)opening portion becomes thinner from the secondary surface of theinsulative substrate toward the main surface; and (ΔW3) is the degree atwhich the (second-1) opening portion becomes thinner from the lowersurface of the second resin insulation layer toward the upper surface.

Accordingly, diameter (Wmin) tends to be enlarged at portion (junction)(33 c) where the first opening portion joins the second opening portion.In addition, diameters of first opening (33A-A) and second opening(33B-B) may be set smaller. Diameter (Wmin) indicates the minimumdiameter of a penetrating hole, corresponding to “Wmin” in FIG. 11.“Wmin” in FIG. 11 is the distance between the portions where the firstopening portion intersects the second opening portion. Since the minimumdiameter of a penetrating hole is enlarged in the first embodiment,cracks seldom occur at junction (33 c) in the through-hole conductor. Inaddition, the diameter of the first opening and the diameter of thesecond opening may be set smaller. The greater of the diameter of thefirst opening and the diameter of the second opening is set as thediameter of the penetrating hole. While preventing a decrease in thereliability of through-hole conductors when their diameters becomesmaller, through-hole conductors are arranged at high density.

FIG. 8(A) shows a penetrating hole of a reference example. In thereference example, the inner walls of first opening portion (333A)change in a straight line. The inner walls of second opening portion(333B) change in a straight line as well. In FIG. 8(B), a penetratinghole of the first embodiment overlaps a penetrating hole of thereference example. The inner walls of the reference example are drawnusing a solid line, and parts of the inner walls of the first embodimentare drawn using a broken line. In the first embodiment, a first openingportion is made up of a (first-1) opening portion and a (first-2)opening portion, and the inner walls of the first opening portion bendat predetermined spots (a, b). The inner walls of the (first-1) openingportion range from the first surface of the core substrate to bentportions (a, b). The inner walls of the (first-1) opening portion aredrawn using broken line “Z.” The inner walls of the (first-2) openingportion range from bent portions (a, b) to bent portions (c, d). Theinner walls of the reference example overlap the inner walls of the(first-2) opening portion in the first embodiment (see FIG. 8(B)). Thefirst opening portion bends toward the inside of the penetrating hole atthe boundary between the (first-1) opening portion and the (first-2)opening portion. The inner walls of a second opening portion bend atpredetermined spots (e, f). The inner walls of the (second-1) openingportion range from the second surface of the core substrate to bentportions (e, f). The inner walls of the (second-1) opening portion aredrawn using broken line “V.” The inner walls of the (second-2) openingportion range from bent portions (e, f) to bent portions (c, d). Theinner walls of the reference example overlap the inner walls of the(second-2) opening portion in the first embodiment (see FIG. 8(B)). Thesecond opening portion bends toward the inside of the penetrating holeat the boundary between the (second-1) opening portion and the(second-2) opening portion.

As shown in FIG. 8(B), if the minimum diameter (Wmin) of a penetratinghole is the same in the reference example and in the first embodiment,diameter (W2) of first opening (33A-A) in the first embodiment is setsmaller than diameter (W1) of the first opening in the referenceexample; and diameter (W3) of second opening (33B-B) in the firstembodiment is set smaller than diameter (W4) of the second opening inthe reference example. Even if the minimum diameter of a penetratinghole in the reference example is the same as the minimum diameter of apenetrating hole in the first embodiment, diameter (WW) of a penetratinghole in the first embodiment is set smaller than the diameter of apenetrating hole in the reference example. The greater of W2 and W3 isset as diameter (WW) of the penetrating hole. Therefore, in the firstembodiment, the diameter of a through-hole conductor (the diameter of apenetrating hole) may be set smaller than that of the reference example.Through-hole conductors may be set at a smaller pitch in the firstembodiment than those in the reference example. The core substrate maybe formed smaller in the first embodiment. The reliability ofthrough-hole conductors in the first embodiment is better than thereliability of through-hole conductors in the reference example.

When the first embodiment and the reference example are compared, sincethe ratio of diameter (WW) of penetrating hole 33 to minimum diameter(Wmin) (Wmin/WW) is greater in the first embodiment, the reliability ofa through-hole conductor is enhanced against core substrate warping orthe like that is caused by thermal contraction.

In FIG. 8(C), a penetrating hole of the first embodiment overlaps apenetrating hole of the reference example. The inner walls in thereference example are drawn using a broken line, and the inner walls ofthe first embodiment are drawn using a solid line. First opening portion(33A) of the first embodiment is made up of the (first-1) openingportion and the (first-2) opening portion, and the inner walls of thefirst opening portion bend at predetermined spots. The inner walls ofthe (first-1) opening portion are drawn using solid line “Z′.” The innerwalls of second opening portion (33B) bend at predetermined spots. Theinner walls of the (second-1) opening portion are drawn using solid line“V′.” As shown in FIG. 8(C), if diameter (W1) of the first opening of apenetrating hole is the same in the reference example and the firstembodiment, minimum diameter (D1) of a penetrating hole in the firstembodiment is greater than minimum diameter (D2) of a penetrating holein the reference example. Namely, in the first embodiment, since theminimum diameter of a penetrating hole is enlarged relative to thediameter of the first opening, the first opening portion and the secondopening portion is joined highly accurately. In addition, since theminimum diameter of a penetrating hole is enlarged, warping in a printedwiring board is suppressed. Furthermore, the reliability of thethrough-hole conductor filled in a penetrating hole is enhanced.

FIG. 9 are cross-sectional views obtained by slicing a core substratewith a plane that includes the first gravity line. The arrow indicatedto the left of the core substrate is axis Z, which is perpendicular tothe first surface of the core substrate. The plus direction goes upwardand the minus direction goes downward. In FIG. 9(A), the core substrateis made of one material. As shown in FIG. 9(A), in the first embodiment,first opening portion (33A) is made up of (first-1) opening portion(33A-1) and (first-2) opening portion (33A-2); and second openingportion (33B) is made up of (second-1) opening portion (33B-1) and(second-2) opening portion (33B-2). A penetrating hole is formed by thefirst opening portion and the second opening portion which are joinedinside the core substrate. The (first-1) opening portion is an openingportion that includes the first opening, and the (first-2) openingportion is an opening portion that is contiguous to the (first-1)opening portion in the core substrate. The (second-1) opening portion isan opening portion that includes the second opening, and the (second-2)opening portion is an opening portion that is contiguous to the(second-1) opening portion in the core substrate. The inner walls of thefirst opening portion bend in the direction of the first gravity line atthe boundary between the (first-1) opening portion and the (first-2)opening portion. The inner walls of the second opening portion bend inthe direction of the first gravity line at the boundary between the(second-1) opening portion and the (second-2) opening portion. The firstopening portion, the (first-1) opening portion and the (first-2) openingportion become gradually thinner from the first surface of the coresubstrate toward the second surface. When the degree at which the(first-1) opening portion becomes thinner is (ΔW1), and the degree atwhich the (first-2) opening portion becomes thinner is (ΔW2), (ΔW2) isset greater than (ΔW1). (ΔW1) and (ΔW2) are the degrees at which the(first-1) opening portion and the (first-2) opening portion becomethinner in the minus direction along axis Z.

(H1) in FIG. 9(A) is the inner diameter of (first-1) opening portion(33A-1), and is the distance between the inner walls facing each otherat predetermined spots in the (first-1) opening portion. The value of(H1) decreases from the first surface of the core substrate toward thesecond surface (the value of (H1) decreases in the minus direction alongaxis Z). The amount of change is (ΔH1). (H2) in FIG. 9(A) is the innerdiameter of (first-2) opening portion (33A-2), and is the distancebetween the inner walls facing each other at predetermined spots in the(first-2) opening portion. The value of (H2) decreases from the firstsurface of the core substrate toward the second surface (the value of(H2) decreases in the minus direction along axis Z). The amount ofchange is (ΔH2). (ΔH2) is set greater than (ΔH1).

Second opening portion (33B), (second-1) opening portion (33B-1) and(second-2) opening portion (33B-2) become gradually thinner from thesecond surface of the core substrate toward the first surface. When thedegree at which the (second-1) opening portion becomes thinner is (ΔW3),and the degree at which the (second-2) opening portion becomes thinneris (ΔW4), (ΔW4) is set greater than (ΔW3). (ΔW3) and (ΔW4) are thedegrees at which the (second-1) opening portion and the (second-2)opening portion become thinner in the plus direction along axis Z.

(H3) in FIG. 9(A) is the inner diameter of (second-1) opening portion(33B-1), and is the distance between the inner walls facing each otherat predetermined spots in the (second-1) opening portion. The value of(H3) decreases from the second surface of the core substrate toward thefirst surface (the value of (H3) decreases in the plus direction alongaxis Z). The amount of change is (ΔH3). (H4) in FIG. 9(A) is the innerdiameter of (second-2) opening portion (33B-2), and is the distancebetween the inner walls facing each other at predetermined spots in the(second-2) opening portion. The value of (H4) decreases from the secondsurface of the core substrate toward the first surface (the value of(H4) decreases in the plus direction along axis Z). The amount of changeis (ΔH4). (ΔH4) is set greater than (ΔH3).

FIG. 9(B) shows an example in which a core substrate is made up of aninsulative substrate and of resin insulation layers sandwiching theinsulative substrate. A (first-1) opening portion is an opening thatpenetrates through a first resin insulation layer, and a (first-2)opening portion is an opening formed in the main-surface side of theinsulative substrate. The (first-1) opening portion becomes graduallythinner from the front surface of the first resin insulation layertoward the back surface with a degree of (ΔW1). The (first-2) openingportion becomes gradually thinner from the main surface of theinsulative substrate toward the secondary surface with a degree of(ΔW2). (ΔW2) is set greater than (ΔW1). (ΔW1) and (ΔW2) are the degreesat which the (first-1) opening portion and the (first-2) opening portionbecome thinner in the minus direction along axis Z. (H1) in FIG. 9(B) isthe inner diameter of the (first-1) opening portion, and is the distancebetween the inner walls facing each other at predetermined spots in the(first-1) opening portion. The value of (H1) decreases from the frontsurface of the first resin insulation layer toward the back surface (thevalue of (H1) decreases in the minus direction along axis Z). (H2) inFIG. 9(B) is the inner diameter of the (first-2) opening portion, and isthe distance between the inner walls facing each other at predeterminedspots in the (first-2) opening portion. The value of (H2) decreases fromthe main surface of the insulative substrate toward the secondarysurface (the value of (H2) decreases in the minus direction along axisZ). A (second-1) opening portion is an opening that penetrates through asecond resin insulation layer, and a (second-2) opening portion is anopening formed in the secondary-surface side of the insulativesubstrate. The (second-1) opening portion becomes gradually thinner fromthe lower surface of the second resin insulation layer toward the uppersurface with a degree of (ΔW3). The (second-2) opening portion becomesgradually thinner from the secondary surface of the insulative substratetoward the main surface with a degree of (ΔW4). (ΔW4) is set greaterthan (ΔW3). (ΔW3) and (ΔW4) are the degrees at which the (second-1)opening portion and the (second-2) opening portion become thinner in theplus direction along axis Z. (H3) in FIG. 9(B) is the inner diameter ofthe (second-1) opening portion, and is the distance between the innerwalls facing each other at predetermined spots in the (second-1) openingportion. The value of (H3) decreases from the lower surface of thesecond resin insulation layer toward the upper surface (the value of(H3) decreases in the plus direction along axis Z). The amount of changeis (ΔH3). (H4) in FIG. 9(B) is the inner diameter of the (second-2)opening portion, and is the distance between the inner walls facing eachother at predetermined spots in the (second-2) opening portion. Thevalue of (H4) decreases from the secondary surface of the insulativesubstrate toward the main surface (the value of (H4) decreases in theplus direction along axis Z). The amount of change is (ΔH4). (ΔH4) isset greater than (ΔH3).

Since the value of (ΔW1) is different from that of (ΔW2) in the firstopening portion, the first opening portion bends at the boundary betweenthe (first-1) opening portion and the (first-2) opening portion. In thesame manner, since the value of (ΔW3) is different from that of (ΔW4) inthe second opening portion, the second opening portion bends at theboundary between the (second-1) opening portion and the (second-2)opening portion.

Since the value of (ΔH1) is different from that of (ΔH2) in the firstopening portion, the first opening portion bends at the boundary betweenthe (first-1) opening portion and the (first-2) opening portion. In thesame manner, since the value of (ΔH3) is different from that of (ΔH4) inthe second opening portion, the second opening portion bends at theboundary between the (second-1) opening portion and the (second-2)opening portion.

When forming opening portions under the same conditions using a laser inan insulative substrate and resin insulation layers that form a coresubstrate, forming opening portions in resin insulation layers ispreferred to be carried out more easily than forming opening portions inthe insulative substrate. A first opening portion and a second openingportion with bent portions may be formed more easily than a coresubstrate that is formed with one material (FIG. 9(A)).

FIG. 10 show through-hole conductors obtained by filling conductor inpenetrating holes in the first embodiment and the reference example(FIGS. 8, 9). FIG. 10(A) shows through-hole conductor 360 of thereference example, and FIGS. 10(B) and 10(E) show through-holeconductors of the first embodiment. In FIGS. 10(B) and 10(E), a firstgravity line and a second gravity line are offset. A core substrate inFIG. 10(B) is made up of an insulative substrate and of a first resininsulation layer and a second resin insulation layer sandwiching theinsulative substrate. A core substrate in FIG. 10(E) is made of onematerial. As a conductor for filling a penetrating hole, plated-metalfilm and conductive paste may be used. As for such plated metal film,electrolytic plated film and electroless plated film may be listed. Asfor such a through-hole conductor, a metal made of a seed layer formedon the inner walls of a penetrating hole and of an electrolytic platedfilm on the seed layer is preferred. Such electrolytic plated film fillsthe penetrating hole. As for a seed layer, sputtered film andelectroless plated film may be listed. Through-hole conductor 36 of thefirst embodiment is made of conductors filled in a (first-1) openingportion, a (first-2) opening portion, a (second-1) opening portion and a(second-2) opening portion. The conductor filled in the (first-1)opening portion becomes thinner from the first surface of the coresubstrate toward the second surface with a degree of (M). The conductorfilled in the (first-2) opening portion becomes thinner from the firstsurface of the core substrate toward the second surface with a degree of(δ2). Since the value of (δ1) is different from that of (δ2), thethrough-hole conductor bends in the core substrate. Accordingly, thethrough-hole conductor in the first opening portion contains bentportion (36 d). The conductor filled in the (second-1) opening portionbecomes thinner from the second surface of the core substrate toward thefirst surface with a degree of (δ4). The conductor filled in the(second-2) opening portion becomes thinner from the second surface ofthe core substrate toward the first surface with a degree of (δ3). Sincethe value of (δ3) is different from that of (δ4), the through-holeconductor bends in the core substrate. Accordingly, the through-holeconductor in the second opening portion contains bent portion (36 e). Ifa core substrate is made of an insulative substrate and of a first resininsulation layer and a second resin insulation layer sandwiching theinsulative substrate, bent portion (36 d) is positioned at the interfaceof the first resin insulation layer and the insulative substrate, andbent portion (36 e) is positioned at the interface of the second resininsulation layer and the insulative substrate. Furthermore, thethrough-hole conductor of the first embodiment contains bent portion (36f) at the junction of the first opening portion and the second openingportion. By contrast, the reference example has neither a (first-2)opening portion nor a (second-2) opening portion. Thus, a through-holeconductor of the reference example contains a bent portion at thejunction of a first opening portion and a second opening portion, butdoes not contain a bent portion at the boundary between a (first-1)opening portion and a (first-2) opening portion or at the boundarybetween a (second-1) opening portion and a (second-2) opening portion.FIGS. 10(C), (D) and (F) show portions where through-hole conductorsbend. Circled portions are bent portions. FIG. 10(C) shows through-holeconductor 360 of the reference example, and FIGS. 10(D) and (F) arethrough-hole conductors 36 of the first embodiment. When a coresubstrate is warped, it is thought that stresses tend to concentrate inbent portions. If the reference example and the first embodiment arecompared in cross-sectional views, the number of bent portions of athrough-hole conductor in the reference example is two, whereas thenumber of bent portions of a through-hole conductor of the firstembodiment is six. A through-hole conductor of the first embodimentcontains more bent portions than a through-hole conductor of thereference example. Therefore, when the first embodiment and thereference example are compared, it is thought that stresses on athrough-hole conductor are dispersed to more portions in the firstembodiment than in the reference example. Accordingly, it is thoughtthat a through-hole conductor of the first embodiment has higherreliability than a through-hole conductor of the reference example. WhenFIGS. 10(D) and 10(F) are compared, strengths in resin insulation layersand an insulative substrate may be modified in FIG. 10(D). Whencomparing the degree at which a through-hole conductor bends at theboundary between a (first-1) opening portion and a (first-2) openingportion, and the degree at which a through-hole conductor bends at thejunction of a first opening portion and a second opening portion, thelatter is greater. The through-hole conductor tends to be damaged at thejunction of the first opening portion and the second opening portion.However, since deformation of an insulative substrate is reduced bysetting the strength of the insulative substrate higher than thestrength of resin insulation layers, stresses that concentrate in thejunction of the first opening portion and the second opening portiondecrease. From such a point of view, it is preferred that a coresubstrate be made of an insulative substrate and of a first resininsulation layer and a second resin insulation layer sandwiching theinsulative substrate, and that the strength of the insulative substratebe set greater than the strength of the first and second resininsulation layers. Accordingly, a through-hole conductor of the firstembodiment is thought to have higher tolerance against stressesgenerated in a warped core substrate or the like than that of thereference example.

If a core substrate is made up of an insulative substrate and of a firstresin insulation layer and a second resin insulation layer sandwichingthe insulative substrate, an ingredient that dissolves in a chemical maybe contained in first resin insulation layer (32A) and second resininsulation layer (32B). By dissolving the soluble ingredient on thesurfaces of resin insulation layers using a chemical, the surfaces ofresin insulation layers may be roughened. By forming roughened surfaces(32α) on the surfaces of core substrate 30, first and second circuitsmay be formed on the first and second surfaces of core substrate 30using an additive method. Since circuits may be formed on the coresubstrate using an additive method and not using a subtractive method,the width of circuits or the distance between circuits may be setsmaller on the core substrate. Accordingly, the number of built-uplayers on the core substrate is reduced.

In the following, a method for manufacturing multilayer printed wiringboard 10 is described with reference to FIGS. 1-5.

(1) Insulative substrate 31 made of reinforcing material and resin isprepared (FIG. 1(A)). The thickness of insulative substrate 31 is set at0.2-0.8 mm. Glass cloth, aramid fiber and glass fiber may be listed as areinforcing material. Glass cloth is preferred as a reinforcing materialfrom a viewpoint of strength. Epoxy resin and BT (bismaleimide triazine)resin may be listed as a resin. Hydroxide particles may be dispersed ina resin. As for hydroxides, metal hydroxides such as Al(OH)3, Mg(OH)2,Ca(OH)2, Ba(OH)2 and the like are preferred. The thermal expansioncoefficient may be set smaller in the insulative substrate. When forminga (first-2) opening portion and a (second-2) opening portion in theinsulative substrate using a laser, values in (ΔW2) and (ΔW4) may be setgreater. Hydroxides are disintegrated by heat, producing water. Thus, itis thought that hydroxides may rob heat from the material that forms aninsulative substrate. Namely, if an insulative substrate contains ahydroxide, it is thought that the insulative substrate is hard toprocess by a laser. Forming a first opening portion made up of a(first-1) opening portion and a (first-2) opening portion as well asforming a second opening portion made up of a (second-1) opening portionand a (second-2) opening portion become easier. When forming openingportions using a CO₂ laser, the insulative substrate is preferred tocontain a hydroxide.

On main surface (31A) and secondary surface (31B) of insulativesubstrate 31, resin film for resin insulation layers 32 (brand name:ABF-45SH, made by Ajinomoto) is laminated. A core substrate made of aninsulative substrate and resin insulation layers is obtained throughthermal pressing (FIG. 1(B)). The core substrate has first surface (30A)and second surface (30B) opposite the first surface. A resin insulationlayer formed on the main surface of insulative substrate 31 is firstresin insulation layer (32A). The first resin insulation layer has afront surface and a back surface opposite the front surface. The backsurface faces the main surface. A resin insulation layer formed underthe secondary surface of insulative substrate 31 is second resininsulation layer (32B). The second resin insulation layer has an uppersurface and a lower surface opposite the upper surface. The secondarysurface faces the upper surface. Resin film for resin insulation layerscontains an ingredient which dissolves in a chemical agent and inorganicparticles for adjusting thermal expansion coefficients. The material forthe first resin insulation layer and the second resin insulation layermay be the same as the material for the insulative substrate. However,the first and second resin insulation layers are preferred not tocontain a reinforcing material, and the insulative substrate ispreferred to contain a reinforcing material. The values of (ΔW1) and(ΔW2) may be modified easily. The values of (ΔW3) and (ΔW4) may bemodified easily. The values of (ΔH 1) and (ΔH2) may be modified easily.The values of (ΔH3) and (ΔH4) may be modified easily.

(2) Using a CO₂ gas laser, by irradiating a laser from first surface(30A) of core substrate 30, first opening portion (33A) is formed in thefirst-surface side of the core substrate (FIG. 1(C)).

(3) Using a CO₂ gas laser, by irradiating a laser from second surface(30B) of core substrate 30, second opening portion (33B) is formed inthe second-surface side of the core substrate. Penetrating hole 33 isformed by the first opening portion and the second opening portion,which are joined in insulative substrate 31 (FIG. 1(D)).

FIGS. 11 and 14 show magnified views of penetrating hole 33 in FIG.1(D). In FIG. 11, a core substrate is made of resin insulation layersand an insulative substrate. The resin insulation layers and insulativesubstrate may be formed with the same material or different materials.Different materials are preferred. In FIG. 14, a core substrate is madeof either one insulative substrate or one resin insulation layer. FIG.11(A) and FIG. 14(A) show examples where the first, second, third andfourth gravity lines overlap each other. FIG. 11(B) and FIG. 14(B) showexamples where the first and third gravity lines overlap each other andthe second and fourth gravity lines overlap each other, but the firstgravity line and the second gravity line are offset from each other.FIG. 11(C) and FIG. 14(C) show examples where the second and fourthgravity lines overlap each other, but the first, second and thirdgravity lines are offset from each other. FIG. 11(D) and FIG. 14(D) showexamples where the first, second, third and fourth gravity lines areoffset from each other. The first opening portion becomes thinner fromthe first surface of the core substrate toward the second surface. InFIG. 11, the inner walls of the first opening portion bend toward theinside of the first opening portion at the interface of the insulativesubstrate and the first resin insulation layer. The second openingportion becomes thinner from the second surface of the core substratetoward the first surface. The inner walls of the second opening portionsbend toward the inside of the opening portion at the interface of theinsulative substrate and the second resin insulation layer. The degreeat which the diameter of first opening portion (33A) decreases is setgreater in insulative substrate 31 than in the first resin insulationlayer. In the same manner, the degree at which the diameter of secondopening portion (33B) decreases is set greater in insulative substrate31 than in the second resin insulation layer.

The first opening portion becomes thinner from the first surface of thecore substrate toward the second surface. In FIG. 14, the inner walls ofthe first opening portion bend toward the inside of the first openingportion at the boundary between the (first-1) opening portion and the(first-2) opening portion. The second opening portion becomes thinnerfrom the second surface of the core substrate toward the first surface.The inner walls of the second opening portion bend toward the inside ofthe second opening portion at the boundary between the (second-1)opening portion and the (second-2) opening portion. The degree at whichthe diameter of first opening portion (33A) decreases is set greater inthe (first-2) opening portion than in the (first-1) opening portion. Inthe same manner, the degree at which the diameter of second openingportion (33B) decreases is set greater in the (second-2) opening portionthan in the (second-1) opening portion.

In the following, a method for forming penetrating holes shown in FIGS.11 and 14 is shown.

Penetrating holes shown in FIGS. 11 and 14 may be formed by a processingmethod as follows. If a first opening portion and a second openingportion are formed by laser irradiations having multiple pulses, thelaser intensity is set lower after a predetermined number of pulses. Forexample, if a first opening portion and a second opening portion areformed by two-pulse laser irradiations, the laser intensity of thesecond pulse is set lower than the laser intensity of the first pulse.Openings to be formed by the first pulse are a (first-1) opening portionand a (second-1) opening portion; openings to be formed by the secondpulse are a (first-2) opening portion and a (second-2) opening portion.In doing so, openings to be formed by the first pulse may be formeddifferently from openings to be formed by the second pulse. Since thesecond pulse has weaker energy than the first pulse, the first openingportion bends inward at the boundary between the (first-1) openingportion and the (first-2) opening portion. In the same manner, thesecond opening portion bends inward at the boundary between the(second-1) opening portion and the (second-2) opening portion. Positionsof gravity lines are modified by adjusting positions to be irradiated bya laser. More detailed descriptions will be provided in the following.

Other examples are shown in the following. If a core substrate is madeof an insulative substrate which is hard to process by a laser and ofresin insulation layers sandwiching the insulative substrate which areeasy to process by a laser, penetrating holes shown in FIG. 11 may beformed. In such examples, when processing resin insulation layers and aninsulative substrate using the same laser intensity, the amount to beprocessed is different in the resin insulation layers and the insulativesubstrate. The amount to be processed is greater in resin insulationlayers than in the insulative substrate. In doing so, openings formed inresin insulation layers may be formed differently from openings formedin the insulative substrate. Openings formed in resin insulation layersare a (first-1) opening portion and a (second-1) opening portion, andopenings formed in the insulative substrate are a (first-2) openingportion and a (second-2) opening portion. Since the insulative substrateis harder to process by a laser than the resin insulation layers are,the first opening portion bends inward at the boundary between the(first-1) opening portion and the (first-2) opening portion. In the samemanner, the second opening portion bends inward at the boundary betweenthe (second-1) opening portion and the (second-2) opening portion. Insuch situations, boundaries are positioned most likely at interfaces ofthe resin insulation layers and the insulative substrate. However,positions for the first opening portion and the second opening portionto bend may be in the insulative substrate, because the same effects asabove are achieved. Combination examples of an insulative substrate andresin insulation layers will be listed in the following. An insulativesubstrate is made of reinforcing material and resin, and resininsulation layers are made of inorganic particles and resin. Since theinsulative substrate contains reinforcing material, the insulativesubstrate is harder to process by a laser than resin insulation layersare. Positions where the first opening portion and the second openingportion bend are preferred to be between an interface of a resininsulation layer and the insulative substrate and a reinforcing materialin the insulative substrate, including an example where opening portionsbend in the reinforcing material (see FIG. 12(C)). Another example maybe such that resin insulation layers contain oxide particles and aninsulative substrate contains hydroxide particles. Since the insulativesubstrate contains hydroxide particles, the insulative substrate isharder to process by a laser than resin insulation layers are. As foroxide particles, alumina, silica, barium oxide or the like may belisted.

The insulative substrate is made of resin and reinforcing material, andresin insulation layers are made of inorganic particles and resinwithout reinforcing material. In such an example, penetrating holesshown in FIG. 11 are obtained as well. Moreover, it is preferred thatthe insulative substrate contain hydroxide particles and that the resininsulation layers not contain hydroxide particles.

Penetrating holes shown in FIG. 11(A) and FIG. 14(A) may be formed bythe following method (method example 1). A first-pulse laser isirradiated in a predetermined spot on the first surface of a coresubstrate. Such a position is set as spot (M). A second-pulse laser isirradiated on the same spot. The first laser pulse has greater energythan the second laser pulse. Accordingly, a first opening portion isformed with a (first-1) opening portion and a (first-2) opening portion.Next, a first-pulse laser is irradiated on the second surface of thecore substrate. The laser position for a first pulse (spot (N)) islocated opposite spot (M). Namely, the laser position for a first pulse(spot (N)) is a point where a straight line passing through spot (M) andperpendicular to the first surface of the core substrate intersects thesecond surface of the core substrate. A second-pulse laser is irradiatedat the same spot. The first laser pulse has greater energy than thesecond laser pulse. The penetrating holes shown in FIG. 11(A) and FIG.14(A) are formed by joining the first opening portion and the secondopening portion. Core substrates which can employ the above method are:core substrate 400 made of resin and inorganic particles; core substrate400 made of resin and reinforcing material; core substrate 400 made ofinorganic particles, resin and reinforcing material; core substrate 400made of hydroxide particles, resin and reinforcing material; and coresubstrate 30 made of an insulative substrate and resin insulation layerssandwiching the insulative substrate. If openings are formed under thesame conditions by a laser in an insulative substrate and resininsulation layers, forming openings in resin insulation layers is easierthan forming openings in the insulative substrate.

A penetrating hole shown in FIG. 11(B) may be formed as follows (methodexample 2). A core substrate shown in FIG. 11(B) is formed with aninsulative substrate which is made of reinforcing material, metalhydroxide and resin, and with resin insulation layers sandwiching theinsulative substrate which are made of inorganic particles and resin. Alaser is irradiated at a predetermined position (spot (O)) on the firstsurface of the core substrate to form first opening portion (33A) madeup of a (first-1) opening portion and a (first-2) opening portion (FIG.15(A)). Next, a laser is irradiated at a predetermined position (spot(P)) on the second surface of the core substrate to form second openingportion (33B) made up of a (second-1) opening portion and a (second-2)opening portion (FIG. 15(B)). Spot (O) and spot (P) do not face eachother. Namely, spot (P) is located at a predetermined distance from thepoint where a straight line passing through spot (O) and perpendicularto the first surface of the core substrate intersects the second surfaceof the core substrate. Accordingly, a penetrating hole shown in FIG.11(B) is formed by the first opening portion and the second openingportion joined in the insulative substrate.

Penetrating holes shown in FIG. 11(C) and FIG. 14(C) may be formed bymodifying method example 1 (method example 3). By shifting the laserposition for a first pulse and the laser position for a second pulse(spot (Q)) to be irradiated on the first surface of a core substrate inmethod example 1, penetrating holes shown in FIG. 11(C) and FIG. 14(C)are formed. A penetrating hole shown in FIG. 11(C) is obtained byjoining a first opening portion and a second opening portion. At thattime, the diameter of the second-pulse laser is preferred to be setsmaller than the diameter of the first-pulse laser.

A penetrating hole in FIG. 11(C) may be formed by modifying methodexample 2 (method example 4). The number of laser pulses to beirradiated on the first surface of a core substrate in method example 2is multiple, the same as in method example 1. By shifting the laserposition for a first pulse (spot (O)) and the laser position for asecond pulse (spot (S)) on the first surface of the core substrate (FIG.15(C)), the penetrating hole shown in FIG. 11(C) is obtained. Thepenetrating hole shown in FIG. 11(C) is obtained by joining a firstopening portion and a second opening portion in the insulativesubstrate. At that time, the diameter of the second-pulse laser ispreferred to be set smaller than the diameter of the first-pulse laser.

The penetrating holes in FIG. 11(D) and FIG. 14(D) may be formed bymodifying method example 3 (method example 5). In method example 5, thelaser position for a second pulse (spot (R)) to be irradiated on thesecond surface of a core substrate is located at a predetermineddistance from the laser position for a first pulse. The penetratingholes shown in FIG. 11(D) and FIG. 14(D) are obtained by joining a firstopening portion and a second opening portion. At that time, the diameterof the second-pulse laser is preferred to be set smaller than thediameter of the first-pulse laser. The following does not overlap eachother: a straight line (straight line M) passing through spot (M) andperpendicular to the first surface of the core substrate; a straightline (straight line N) passing through spot (N) and perpendicular to thefirst surface of the core substrate; a straight line (straight line Q)passing through spot (Q) and perpendicular to the first surface of thecore substrate; and a straight line (straight line R) passing throughspot (R) and perpendicular to the first surface of the core substrate(FIG. 15(D)).

A penetrating hole in FIG. 11(D) may be formed by modifying methodexample 4 (method example 6). In method example 6, the number of laserpulses to be irradiated on the second surface of a core substrate ismultiple. The laser position (spot (R)) for a second pulse to beirradiated on the second surface of the core substrate is located at apredetermined distance from the laser position for a first pulse. Atthat time, the diameter of the second pulse is preferred to be setsmaller than the diameter of the first pulse. The penetrating hole inFIG. 11(D) is obtained by joining the first opening portion and thesecond opening portion. The following does not overlap each other: astraight line (straight line O) passing through spot (O) andperpendicular to the first surface of the core substrate; a straightline (straight line P) passing through spot (P) and perpendicular to thefirst surface of the core substrate; a straight line (straight line S)passing through spot (S) and perpendicular to the first surface of thecore substrate; and a straight line (straight line R) passing throughspot (R) and perpendicular to the first surface of the core substrate.

In any of the method examples, it is preferable to irradiate a laserhaving energy intensities shown in FIG. 12(A) and (B). The lengths inthe drawing schematically indicate laser intensity. The intensity isgreater in the center than on the periphery. Laser intensity decreasesfrom the center toward the periphery either exponentially or in astraight line.

When the laser irradiation position to form a (first-1) opening portionand the laser irradiation position to form a (first-2) opening portionare located at a predetermined distance from each other for offsettingthe first gravity line and the third gravity line, the laser diameterfor forming the (first-1) opening portion is preferred to be set greaterthan the laser diameter for forming the (first-2) opening portion.

When the laser irradiation position to form a (second-1) opening portionand the laser irradiation position to form a (second-2) opening portionare located at a predetermined distance from each other for offsettingthe second gravity line and the fourth gravity line, the laser diameterfor forming the (second-1) opening portion is preferred to be setgreater than the laser diameter for forming the (second-2) openingportion.

(4) Core substrate 30 with penetrating hole 33 is immersed for 10minutes in an 80° C. solution containing 60 g/L permanganic acid.Roughened surfaces (32α) are formed on the surfaces of resin insulationlayers 32 (FIG. 1(E)). The first surface and the second surface of thecore substrate are roughened.

(5) Palladium catalyst (made by Atotech) is attached to the surfaces ofcore substrate 30. After that, the core substrate is immersed in anelectroless plating solution. Electroless plated film 23 is formed onthe first and second surfaces of the core substrate and on the innerwalls of the penetrating hole (see FIG. 2(A)). As for such electrolessplated film, electroless copper-plated film and electrolessnickel-plated film may be listed. The thickness is 0.2 μm-0.6 μm.Plating resist 25 is formed on electroless plated film 23 (FIG. 2(B)).Using electroless plated film as a seed layer, electrolytic plated filmis formed on the electroless plated film left exposed by the platingresist. Penetrating hole 33 is filled with electrolytic plated film 24(FIG. 2(C)). Instead of electroless plated film, sputtered film may beformed on the inner walls of penetrating hole 33 and on the surfaces ofthe core substrate.

(6) Plating resist is removed. The electroless plated film exposed byremoving the plating resists is etched away. First circuit (34A) isformed on the first surface of the core substrate. Second circuit (34B)is formed on the second surface of the core substrate (see FIG. 3(A)).Printed wiring board 1000 is completed. The first circuit has firstconductive circuit (34AC) and first through-hole land (first land)(34AL). The first conductive circuit is a circuit that is formed on thefirst surface of the core substrate, and first through-hole land (34AL)is formed with a circuit covering a through-hole conductor and a circuitformed on the first surface of the core substrate surrounding thethrough-hole conductor. The second circuit has second conductive circuit(34BC) and second through-hole land (second land) (34BL). Secondconductive circuit (34BC) is a circuit that is formed on the secondsurface of the core substrate, and second through-hole land (34BL) isformed with a circuit covering a through-hole conductor and a circuitformed on the second surface of the core substrate surrounding thethrough-hole conductor.

In the above example, a core substrate is formed with resin insulationlayers and an insulative substrate. However, the core substrate may beformed only with an insulative substrate or a resin insulation layer.The manufacturing method is simplified. Instead of the above method(FIGS. 1 through 3(A)), another method for manufacturing a printedwiring board is shown in FIG. 13. In that example, one insulativesubstrate or one resin insulation layer is a starting material (FIG.13(A)). Copper foils 401 are laminated on single insulative substrate(400A) or single resin insulation layer (400A) (FIG. 13(B)). A laser isirradiated on first surface (30A) of the single insulative substrate orthe single resin insulation layer. First opening portion (33A) is formedin the first-surface side of the single insulative substrate or thesingle resin insulation layer (FIG. 13(C)). A laser is irradiated onsecond surface (30B) of the single insulative substrate or the singleresin insulation layer. Second opening portion (33B) is formed in thesecond-surface side of the single insulative substrate or the singleresin insulation layer. Penetrating hole 33 is formed by first openingportion (33A) and second opening portion (33B), which are joined in thesingle insulative substrate or the single resin insulation layer (FIG.13(D)). A core substrate with a penetrating hole is completed. Thepenetrating hole may be formed by any of the above methods. Seed layer323 is formed on the surfaces of the core substrate and on the innerwalls of the penetrating hole by electroless plating or the like.Electrolytic plated film 324 is formed on seed layer 323. Penetratinghole 33 is filled with electrolytic plated film 324 (FIG. 13(E)). Byforming conductive circuits (34AC, 34BC) and lands (34AL, 34BL) on thecore substrate by etching, printed wiring board 1000 is completed (FIG.13(F)).

(9) Next, roughened layers (34β) are formed on the surfaces of first andsecond circuits (34A, 34B) (FIG. 3(B)).

(10) On both surfaces of core substrate 30 having circuits, resin filmfor interlayer resin insulation layers (brand name: ABF-45SH, made byAjinomoto) is laminated. By curing the film, interlayer resin insulationlayers (50A, 50B) are formed on both surfaces of the core substrate(FIG. 3(C)).

(11) Via-conductor openings 51 reaching conductive circuits orthrough-hole lands are formed in interlayer resin insulation layers(50A, 50B) using a CO₂ gas laser (FIG. 3(D)).

(12) The substrate with via-conductor openings 51 is immersed for 10minutes in an 80° C. solution containing 60 g/L permanganic acid.Roughened surfaces (50α) are formed on the surfaces of interlayer resininsulation layers (50A, 50B) including the inner walls of via-conductoropenings 51 (FIG. 4(A)). By immersing the substrate in a catalystsolution, catalyst nuclei are attached on the surfaces of interlayerresin insulation layers and on the inner-wall surfaces of via-conductoropenings.

(13) Next, by immersing the substrate in an electroless copper platingsolution (Thru-Cup PEA) made by C. Uyemura Co., Ltd., electrolesscopper-plated film 52 is formed on the surfaces of interlayer resininsulation layers (50A, 50B) including the inner walls of via-conductoropenings 51 (FIG. 4(B)).

(14) Plating resist 54 is formed on electroless copper-plated film 52.Electrolytic copper-plated film 56 is formed on the electroless platedfilm left exposed by plating resist 54 (FIG. 4(C)).

(15) Plating resist 54 is removed. By removing the electroless platedfilm between portions of electrolytic copper-plated film throughetching, independent conductive circuits (58A, 58B) and via conductors(60A, 60B) are formed (FIG. 4(D)). Multilayer wiring board 300 isobtained.

(16) Roughened layers (58α) are formed on the surfaces of conductivecircuits (58A, 58B) and via conductors (60A, 60B) (FIG. 5(A)).

(18) Next, solder-resist layers (70A, 70B) with openings (71A, 71B) areformed on both surfaces of multilayer wiring board 300 (FIG. 5(B)). Topsurfaces of conductive circuits (58A, 58B) and via conductors (60A, 60B)are exposed through openings (71A, 71B). Top surfaces of conductivecircuits (58A, 58B) and via conductors (60A, 60B) exposed throughopenings (71A, 71B) function as solder pads (72A, 72B).

(19) A nickel-plated layer is formed on solder pads, and a gold-platedlayer is formed on the nickel-plated layer (FIG. 5(C)). Instead ofnickel-gold layers, nickel-palladium-gold layers may also be formed onsolder pads.

(21) After that, solder balls are loaded on opening portions (71A, 71B)in the solder-resist layers, and reflowed at 230° C. Accordingly, solderbumps (78A, 78B) are formed on solder pads (FIG. 6).

First Example

(1) Insulative substrate 31 made of glass cloth, epoxy resin andmagnesium hydroxide is prepared (FIG. 1(A)). The thickness of insulativesubstrate 31 is 0.2 mm. Insulative substrate 31 has main surface (31A)and secondary surface (31B) opposite the main surface. Resin film forresin insulation layers 32 (brand name: ABF-45SH, made by Ajinomoto) islaminated on both surfaces of the insulative substrate. By thermalpressing the film, a core substrate formed with an insulative substrateand resin insulation layers is obtained (FIG. 1(B)). Resin insulationlayers contain ingredients that dissolve in a KMnO4 solution and silicafor adjusting thermal expansion coefficients. The first resin insulationlayer and the second resin insulation layer do not contain reinforcingmaterial.

(2) A CO₂ gas laser is irradiated at a predetermined position (spot 1)on first surface (30A) of core substrate 30. The number of laser pulsesto be irradiated is four. First opening portion (33A) made up of a(first-1) opening portion and a (first-2) opening portion is formed inthe first-surface side of the core substrate (FIG. 1(C)). The (first-1)opening portion is an opening portion formed in the first resininsulation layer, and the (first-2) opening portion is an openingportion formed in the insulative substrate. Since first resin insulationlayer (32A) tends to be processed by a laser more easily than insulativesubstrate 31, the first opening portion bends inward at the boundarybetween the (first-1) opening portion and the (first-2) opening portion.The bent positions are located substantially at the interface of firstresin insulation layer (32A) and insulative substrate 31.

(3) A CO₂ gas laser is irradiated at a predetermined position (spot 2)on second surface (30B) of core substrate 30. Spot 2 is where a straightline passing through spot 1 and perpendicular to the first surface ofthe core substrate intersects the second surface of the core substrate.The first gravity line overlaps the second gravity line. The number oflaser pulses is four. Second opening portion (33B) made up of a(second-1) opening portion and a (second-2) opening portion is formed inthe second-surface side of the core substrate (FIG. 1(D)). A penetratinghole is formed by joining the first opening portion and the secondopening portion. The (second-1) opening portion is an opening portionformed in the second resin insulation layer and the (second-2) openingportion is an opening portion formed in the insulative substrate. Sincesecond resin insulation layer (32B) tends to be processed by a lasermore easily than insulative substrate 31, the second opening portionbends inward at the boundary between the (second-1) opening portion andthe (second-2) opening portion. The bent positions are locatedsubstantially at the interface of second resin insulation layer (32B)and insulative substrate 31. A penetrating hole shown in FIG. 11(A) isformed.

(4) Core substrate 30 with penetrating hole 33 is immersed for 10minutes in an 80° C. solution containing 60 g/L permanganic acid.Roughened surfaces (32α) are formed on the surfaces of resin insulationlayers 32 (FIG. 1(E)). The first surface and the second surface of thecore substrate are roughened.

(5) A palladium catalyst (made by Atotech) is attached to the surfacesof core substrate 30. Then, the core substrate is immersed in anelectroless copper-plating solution (made by C. Uyemura Co., Ltd.).Electroless copper-plated film 23 is formed on the first and secondsurfaces of the core substrate and on the inner walls of the penetratinghole (see FIG. 2(A)). The thickness of the electroless copper-platedfilm is 0.4 μm. Plating resist 25 is formed on electroless plated film23 (FIG. 2(B)). Electrolytic copper-plated film 24 is formed on theelectroless plated film left exposed by plating resist 25 usingelectroless plated film 23 as a seed layer. Penetrating hole 33 isfilled with electrolytic copper-plated film 24 (FIG. 2(C)).

(6) The plating resist is removed. Electroless copper-plated filmexposed by removing the etching resist is etched away. First conductivecircuit (34AC) and first through-hole land (34AL) are formed on thefirst surface of the core substrate, and second conductive circuit(34BC) and second through-hole land (34BL) are formed on the secondsurface of the core substrate. Simultaneously, through-hole conductor 36is formed, connecting the first and second conductive circuits (see FIG.3(A)). The thickness of electrolytic copper-plated film is substantially15 μm. Printed wiring board 1000 of the first example is completed.

Second Example

(1) Prepreg 400 made of glass cloth and epoxy resin is prepared (FIG.13(A)). On both surfaces of the prepreg, 12 μm-thick copper foil 401 islaminated. By thermal pressing, the prepreg is cured, and core substrate30 having copper foil is obtained (FIG. 13(B)).

(2) A CO₂ gas laser is irradiated at a predetermined position (spot 10)on first surface (30A) of core substrate 30. The number of laser pulsesto be irradiated is four. The laser intensity for the first pulse is setequal to that for the second pulse, and the laser intensity for thethird pulse is set equal to that for the fourth pulse. The laserintensity for the first pulse is set higher than the laser intensity forthe third pulse. The irradiation position (spot 10) is the same for allpulses. First opening portion (33A) made up of (first-1) opening portion(33A-1) and (first-2) opening portion (33A-2) is formed in thefirst-surface side of the core substrate (FIG. 13(C)). Since the laserintensity is set lower on and after the third pulse, first openingportion (33A) bends inward at the boundary between (first-1) openingportion (33A-1) and (first-2) opening portion (33A-2).

A CO₂ gas laser is irradiated at a predetermined position (spot 11) onsecond surface (30B) of core substrate 30. The number of laser pulses tobe irradiated is four. The laser intensity for the first pulse is setequal to that for the second pulse, and the laser intensity for thethird pulse is set equal to that for the fourth pulse. The laserintensity for the first pulse is set greater than the laser intensityfor the third pulse. The irradiation position (spot 11) is the same forall pulses. Second opening portion (33B) made up of (second-1) openingportion (33B-1) and (second-2) opening portion (33B-2) is formed in thesecond-surface side of the core substrate. Penetrating hole 33 made upof the first opening portion and the second opening portion is formed(FIG. 13(D)). The point where a straight line passing through spot 10and perpendicular to the first surface of the core substrate intersectsthe second surface of the core substrate is located at a predetermineddistance from spot 11. Since the laser intensity is set lower on andafter the third pulse, the second opening portion bends inward at theboundary between the (second-1) opening portion and the (second-2)opening portion. Penetrating hole 33 is formed as shown in FIG. 14(B).

Copper film 323 is formed by sputtering on the first and second surfacesof the core substrate and on the inner walls of the penetrating hole.Using copper film 323 as a seed layer, electrolytic copper-plated film324 is formed on the first and second surfaces of the core substrate.Simultaneously, penetrating hole 33 is filled with electrolyticcopper-plated film 324 (FIG. 13(E)). Etching resist is formed on theelectrolytic copper-plated film. The electrolytic copper-plated film,copper film and copper foil left exposed by the etching resist areetched away.

First conductive circuit (34AC) and first through-hole land (34AL) areformed on the first surface of the core substrate, and second conductivecircuit (34BC) and second through-hole land (34BL) are formed on thesecond surface of the core substrate. Simultaneously, through-holeconductor 36 is formed, connecting the first and second conductivecircuits. The thickness of the electrolytic copper-plated film issubstantially 15 μm. Printed wiring board 1000 of the second example iscompleted (FIG. 13(F)).

Third Example

The method for manufacturing a printed wiring board according to thethird example is a modified example of the first example.

The method for forming a core substrate of the third example is the sameas in the first example. First and second laser pulses are irradiated ata predetermined position (spot 10) on the first surface of the coresubstrate. Then, third and fourth laser pulses are irradiated at aposition (spot 100) which is located at a predetermined distance fromspot 10. The laser intensity for the first pulse is set equal to thatfor the second pulse, and the laser intensity for the third pulse is setequal to that for the fourth pulse. The laser intensity for the firstpulse is set greater than the laser intensity for the third pulse. Thediameter of the first laser pulse is equal to that of the second laserpulse, and the diameter of the third laser pulse is equal to that of thefourth laser pulse. The diameter of the first laser pulse is set greaterthan that of the third laser pulse.

First through fourth laser pulses are irradiated at a predeterminedposition (spot 20) on the second surface of the core substrate. A point(point of intersection 1) where a straight line passing through spot 10and perpendicular to the first surface of the core substrate intersectsthe second surface of the core substrate is located at a predetermineddistance from spot 20. In addition, point (point of intersection 2)where a straight line passing through spot 100 and perpendicular to thefirst surface of the core substrate intersects the second surface of thecore substrate is located at a predetermined distance from spot 20.Point of intersection 1, point of intersection 2 and spot 20 do notoverlap. The laser intensity for the first pulse is set equal to thatfor the second pulse, and the laser intensity for the third pulse is setequal to that for the fourth pulse. The laser intensity for the firstpulse is set greater than that for the third laser pulse. A penetratinghole shown in FIG. 11(C) is formed.

Fourth Example

The method for manufacturing a printed wiring board according to thefourth example is a modified example of the third example.

The method for forming a core substrate of the fourth example is thesame as in the first example. First and second laser pulses areirradiated at a predetermined position (spot 10) on the first surface ofthe core substrate. Then, third and fourth laser pulses are irradiatedat a position (spot 100) which is located at a predetermined distancefrom spot 10. The laser intensity for the first pulse is set equal tothat for the second pulse, and the laser intensity for the third pulseis set equal to that for the fourth pulse. The laser intensity for thefirst pulse is set greater than the laser intensity for the third pulse.The diameter of the first laser pulse is equal to that of the secondlaser pulse, and the diameter of the third laser pulse is equal to thatof the fourth laser pulse. The diameter of the first laser pulse isgreater than that of the third laser pulse.

First and second laser pulses are irradiated at a predetermined position(spot 20) on the second surface of the core substrate. Then, third andfourth laser pulses are irradiated at a position (spot 200) which islocated at a predetermined distance from spot 20. A point (point ofintersection 1) where a straight line passing through spot 10 andperpendicular to the first surface of the core substrate intersects thesecond surface of the core substrate is located at predetermineddistances from spot 20 and spot 200. In addition, point (point ofintersection 2) where a straight line passing through spot 100 andperpendicular to the first surface of the core substrate intersects thesecond surface of the core substrate is located at predetermineddistances from spot 20 and spot 200. Point of intersection 1, point ofintersection 2, spot 20 and spot 200 do not overlap. The laser intensityfor the first pulse is set equal to that for the second pulse, and thelaser intensity for the third pulse is set equal to that for the fourthpulse. The laser intensity for the first pulse is set greater than thatfor the third pulse. The diameter of the first laser pulse is setgreater than that of the third laser pulse. A penetrating hole shown inFIG. 11(D) is formed.

Example of Built-Up Wiring Board

Printed wiring board 1000 according to any one of the first through thefourth examples may be used as a core substrate in a built-up wiringboard.

On both surfaces of a printed wiring board according to any one of thefirst through fourth examples, resin film for interlayer resininsulation layers (brand name: ABF-45SH, made by Ajinomoto) islaminated. By curing the film, interlayer resin insulation layers (50A,50B) are formed on both surfaces of a core substrate (FIG. 3(C)).

(11) Using a CO₂ gas laser, via-conductor openings 51 are formed ininterlayer resin insulation layers (50A, 50B), reaching conductivecircuits or through-hole lands (FIG. 3(D)).

(12) The substrate with via-conductor openings 51 is immersed for 10minutes in an 80° C. solution containing 60 g/L permanganic acid.Roughened surfaces (50α) are formed on the surfaces of interlayer resininsulation layers (50A, 50B) including inner walls of via-conductoropenings 51 (FIG. 4(A)). By immersing the substrate in a catalystsolution, catalyst nuclei are attached to the surfaces of the interlayerresin insulation layers and to inner-wall surfaces of the via-conductoropenings.

(13) Next, by immersing the substrate in an electroless copper platingsolution (Thru-Cup PEA) made by C. Uyemura Co., Ltd., electrolesscopper-plated film 52 is formed on the surfaces of interlayer resininsulation layers (50A, 50B) including the inner walls of via-conductoropenings 51 (FIG. 4(B)).

(14) Plating resist 54 is formed on electroless copper-plated film 52.Electrolytic copper-plated film 56 is formed on the electroless platedfilm left exposed by plating resist 54 (FIG. 4(C)).

(15) Plating resist 54 is removed. By etching away the electrolessplated film between portions of electrolytic copper-plated film,independent conductive circuits (58A, 58B) and via conductors (60A, 60B)are formed (FIG. 4(D)). Multilayer wiring board 300 is obtained.

(16) Next, roughened surfaces (58α) are formed on the surfaces ofconductive circuits (58A, 58B) and via conductors (60A, 60B) (FIG.5(A)).

(18) Next, solder-resist layers (70A, 70B) with openings (71A, 71B) areformed on both surfaces of the multilayer wiring board (FIG. 5(B)). Topsurfaces of conductive circuits (58A, 58B) and via conductors (60A, 60B)are exposed through openings (71A, 71B). Top surfaces of conductivecircuits (58A, 58B) and via conductors (60A, 60B) exposed throughopenings (71A) work as solder pads.

(19) A nickel-plated layer is formed on solder pads, and a gold-platedlayer is formed on the nickel-plated layer (FIG. 5(C)).

(21) After that, solder balls are loaded on opening portions (71A, 71B)in the solder-resist layers, and reflowed at 230° C. Accordingly, solderbumps (78A, 78B) are formed on solder pads (FIG. 6). A built-up wiringboard is completed.

Second Embodiment

A multilayer printed wiring board according to the second embodiment ofthe present invention is described with reference to FIG. 16. In amultilayer printed wiring board according to the first embodiment,plating is filled in penetrating hole 33 of a core substrate. Bycontrast, in the second embodiment, through-hole conductor 36 is formedon the side wall of penetrating hole 33, and the inside of through-holeconductor 36 is filled with filling resin 37. The reliability of athrough-hole conductor is also enhanced in a printed wiring board whereresin is filled in the through-hole conductor as shown in the secondembodiment.

A printed wiring board of the present invention has the following: acore substrate with a first surface and a second surface opposite thefirst surface and having a penetrating hole made up of a first openingportion which is formed in the first-surface side and becomes thinnerfrom the first surface toward the second surface and of a second openingportion which is formed in the second-surface side and becomes thinnerfrom the second surface toward the first surface; a first circuit formedon the first surface of the core substrate; a second circuit formed onthe second surface of the core substrate; and a through-hole conductorformed in the penetrating hole and connecting the first circuit and thesecond circuit. In such a printed wiring board, the first openingportion has a first opening on the first surface of the core substrate,the first opening portion is made up of a (first-1) opening portionwhich includes the first opening and of a (first-2) opening portioncontiguous to the (first-1) opening portion, the second opening portionhas a second opening on the second surface of the core substrate, thesecond opening portion is made up of a (second-1) opening portion whichincludes the second opening and of a (second-2) opening portioncontiguous to the (second-1) opening portion, inner walls of the firstopening portion bend toward the inside of the penetrating hole at theboundary between the (first-1) opening portion and the (first-2) openingportion, and inner walls of the second opening portion bend toward theinside of the penetrating hole at the boundary between the (second-1)opening portion and the (second-2) opening portion.

Obviously, numerous modifications and variations of the presentinvention are possible in light of the above teachings. It is thereforeto be understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically describedherein.

1-14. (canceled)
 15. A method for manufacturing a printed wiring board,comprising: preparing a core substrate having a first surface and asecond surface on an opposite side of the first surface and comprising afirst insulation layer, a second insulation layer and an insulativesubstrate interposed between the first insulation layer and the secondinsulation layer; forming a penetrating hole having a first openingportion and a second opening portion in the core substrate such that thefirst opening portion becomes thinner from the first surface of the coresubstrate toward the second surface and that the second opening portionbecomes thinner from the second surface of the core substrate toward thefirst surface; forming a first circuit on the first surface of the coresubstrate; forming a second circuit on the second surface of the coresubstrate; and forming a plated film in the penetrating hole such that athrough-hole conductor connecting the first circuit and the secondcircuit is formed, wherein the first insulation layer comprises a resinmaterial which is easier to be processed by a laser than a resinmaterial of the insulative substrate when the first opening portion isformed under same conditions of the laser for the first insulation layerand the insulative substrate, and the second insulation layer comprisesa resin material which is easier to be processed by a laser than thematerial of the insulative substrate when the second opening portion isformed under same conditions of the laser for the second insulationlayer and the insulative substrate.
 16. The method for manufacturing aprinted wiring board according to claim 15, wherein the preparing of thecore substrate comprises providing the insulative substrate having amain surface and a secondary surface on an opposite side of the mainsurface, laminating the first insulation layer such that the firstinsulation layer faces the main surface of the insulative substrate, andlaminating the second insulation layer such that the second insulationlayer faces the secondary surface of the insulative substrate.
 17. Themethod for manufacturing a printed wiring board according to claim 15,wherein the forming of the penetrating hole comprises forming the firstopening portion by irradiating a laser on the first surface of the coresubstrate and forming the second opening portion by irradiating a laseron the second surface of the core substrate.
 18. The method formanufacturing a printed wiring board according to claim 15, wherein theinsulative substrate includes a reinforcing material.
 19. The method formanufacturing a printed wiring board according to claim 15, wherein thefirst insulation layer includes an inorganic filler, and the secondinsulation layer includes an inorganic filler.
 20. The method formanufacturing a printed wiring board according to claim 15, wherein theinsulative substrate includes a reinforcing material, the firstinsulation layer includes an inorganic filler, the second insulationlayer includes an inorganic filler, and the first insulation layer andthe second insulation layer do not include a reinforcing material. 21.The method for manufacturing a printed wiring board according to claim15, wherein the first opening portion is formed by irradiating a CO₂ gaslaser on the first surface of the core substrate, and the second openingportion is formed by irradiating a CO₂ gas laser on the second surfaceof the core substrate.
 22. The method for manufacturing a printed wiringboard according to claim 16, wherein the insulative substrate includes areinforcing material.
 23. The method for manufacturing a printed wiringboard according to claim 22, wherein the first insulation layer includesan inorganic filler, and the second insulation layer includes aninorganic filler.
 24. The method for manufacturing a printed wiringboard according to claim 23, wherein the first insulation layer and thesecond insulation layer do not include a reinforcing material.
 25. Themethod for manufacturing a printed wiring board according to claim 22,wherein the reinforcing material is a glass cloth.
 26. The method formanufacturing a printed wiring board according to claim 15, wherein astraight line passing through the gravity center of the first openingand perpendicular to the first surface of the core substrate is notaligned with a straight line passing through the gravity center of thesecond opening and perpendicular to the first surface of the coresubstrate.
 27. The method for manufacturing a printed wiring boardaccording to claim 15, wherein the forming of the plated film in thepenetrating hole comprises filling the penetrating hole with a platingmaterial such that the through-hole conductor made of the plated filmfilling the penetrating hole is formed.
 28. The method for manufacturinga printed wiring board according to claim 22, wherein the reinforcingmaterial is an aramid fiber material.
 29. The method for manufacturing aprinted wiring board according to claim 15, wherein the first insulationlayer and the second insulation layer do not include a reinforcingmaterial.
 30. The method for manufacturing a printed wiring boardaccording to claim 15, wherein the first insulation layer includes aninorganic filler comprising at least one of silica and alumina, and thesecond insulation layer includes an inorganic filler comprising at leastone of silica and alumina.
 31. The method for manufacturing a printedwiring board according to claim 15, wherein the first opening portion isformed by irradiating a CO₂ gas laser on the first surface of the coresubstrate, and the second opening portion is formed by irradiating a CO₂gas laser on the second surface of the core substrate, and a straightline passing through the gravity center of the first opening andperpendicular to the first surface of the core substrate is not alignedwith a straight line passing through the gravity center of the secondopening and perpendicular to the first surface of the core substrate.32. The method for manufacturing a printed wiring board according toclaim 15, wherein the forming of the penetrating hole comprises formingthe first opening portion by irradiating a laser on the first surface ofthe core substrate and forming the second opening portion by irradiatinga laser on the second surface of the core substrate, and a straight linepassing through the gravity center of the first opening andperpendicular to the first surface of the core substrate is not alignedwith a straight line passing through the gravity center of the secondopening and perpendicular to the first surface of the core substrate.